Counterbalance valves are hydraulic valves configured to hold and control negative or gravitational loads. They may be configured to operate, for example, in applications that involve the control of suspended loads, such as mechanical joints, lifting applications, extensible movable bridge, winches, etc.
In some applications, the counterbalance valve, which may also be referred to as an overcenter valve, could be used as a safety device that prevents an actuator from moving if a failure occurs (e.g., a hose burst) or could be used as a load holding valve (e.g., on a boom cylinder of a mobile machinery). The counterbalance valve allows cavitation-free load lowering, preventing the actuator from overrunning when pulled by the load (gravitational load).
As an example, a pilot-operated counterbalance valve could be used on the return side of a hydraulic actuator for lowering a large negative load in a controlled manner. The counterbalance valve generates a preload or back-pressure in the return line that acts against the main drive pressure so as to maintain a positive load, which therefore remains controllable. Particularly, if a speed of a piston of the cylinder increases, pressure on one side of the cylinder (e.g., rod side) may drop and the counterbalance valve may then act to restrict the flow to controllably lower the load.
When a directional control valve is operating in a load-lowering mode, the pilot-operated counterbalance valve is opened by a pressurized pilot line. To protect both directions of motion of a fluid receiving device against a negative load, a counterbalance valve may be assigned to each of the ports of the fluid receiving device. Each counterbalance valve assigned to a particular port may then be controlled open via cross-over by the pressure present at the other port. In other words, a respective pressurized pilot line that, when pressurized, opens a counterbalance valve is connected to a supply line connected to the other port.